The present invention relates to an apparatus for making connecting pipes for connecting ducts used in air conditioning systems, etc.
Although a conventional spiral pipe for connecting ducts made of aluminum and having corrugations for reinforcement has an advantage that it can be easily bent, it has a disadvantage in that the air flowing through it encounters remarkably large resistance and produces whistling sounds because of friction with the undulatory internal surface of the corrugations.
In order to eliminate the above-described disadvantage, it has been proposed to form an elbow type connecting pipe by rolling a plurality of strips cut from a flat iron plate into barrels. The barrels can then be welded together. However, this work has to be done by inefficient manual labor resulting in a high manufacturing cost.